1. Field of the Invention
The present invention relates to a roller of a moving body, which rolls on a rail so as to move the moving body along the rail, a moving body having the roller, and a method of producing the roller.
2. Description of Background Art
A conventional roller (roller unit) used in a linear drive unit is disclosed in Japanese Patent Gazette No. 2000-120672. The conventional roller is shown in FIG. 8.
As shown in FIG. 8, the roller unit has a roller member 69, which further acts as an outer retainer. The roller member 69 is made of ceramic and has an outer circumferential face including a rolling face 69c, which contacts a guide face of a linear motion mechanism. Orbital faces 69a and 69b for guiding spherical bodies (balls) 67 are formed in an inner circumferential face of the roller member 69.
Inner retainers 62 and 63 of the roller unit are fitted to one end of a fixed shaft 61. The balls 67 are held between the roller member 69 and the inner retainers 62 and 63. With this structure, the roller member 69 can be freely rotated.
Japanese Patent Gazette No. 2000-120672 further discloses a roller unit including a roller member made of a ferrous material, which contacts a rail (see paragraph 0002 and FIG. 2).
The roller member, whose surface contacting the rail is composed of ceramic or metal, has superior rigidity and abrasion resistance. Therefore, in case of linearly conveying a heavy matter, e.g., 50 kg-several hundred kg, the heavy matter can be smoothly linearly moved without deforming the roller member.
In case of linearly moving a light matter, e.g., 20 kg or less, the surface of the roller member may be composed of synthetic resin.
Japanese Patent Gazette No. 11-351249 discloses a roller unit for linearly moving a relatively light matter, e.g., a slide door of an automobile. A surface of a roller is composed of synthetic resin. The roller unit is shown in FIG. 9.
In the roller unit A shown in FIG. 9, a metallic roller bearing 82 is attached to a shaft 81. Circular grooves 89 are formed in an outer circumferential face of an outer retainer 85 of the roller bearing 82, and a resin coat section 83 composed of synthetic resin is formed, by insert molding, so as to continuously cover the outer circumferential face of the outer retainer 85 and both end faces thereof.
The roller unit A shown in FIG. 9 has the resin coat section 83, which contacts a rail, so that a moving body can be smoothly guided. Further, the circular grooves 89 are formed in the outer circumferential face of the outer retainer 85 and the resin coat section 83 engages with the circular grooves 89, so that the resin coat section 83 can be securely fitted to the roller bearing 82.
However, in the conventional roller shown in FIG. 8, the surface of the roller is composed of ceramic or metal, so the rail will be easily abraded or damaged by the roller. To solve this problem, rigidity of the rail must be increased. By increasing the rigidity of the rail, weight and production cost of the roller unit must be increased.
On the other hand, in the conventional roller shown in FIG. 9, if the roller unit is used to linearly move a heavy matter, e.g., 50 kg-several hundred kg, the resin coat section 83 is deformed by the weight of the heavy matter. By deforming the resin coat section 83, dynamic resistance of the moving unit must be enormously increased and the resin coat section 83 will be detached from the circular grooves 89 or broken.
Generally, a roller having a resin coat section has problems of easily deforming, detaching and breaking the resin coat section, so the roller is not suitable for moving heavy matters.